Callaway Energy Center (Fair Values Of Investments In Debt And Equity Securities In Nuclear Decommissioning Trust Fund) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Nuclear Waste Matters [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 382
Cash and cash equivalents	272	$ 216	$ 155	$ 301
Fair Value	1,150	958
Cash and cash equivalents	25	10
Ameren Missouri
Nuclear Waste Matters [Line Items]
Debt, Equity, Marketable, And Other Securities, Available-For-Sale, Amortized Cost	582	562
Cash and cash equivalents	10	13	$ 8	$ 145
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	606	455
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	38	59
Fair Value	1,150	958
Cash and cash equivalents	0	0
Debt, Equity, Marketable, And Other Securities, Available-For-Sale	1,150	958
Ameren Missouri | Debt securities
Nuclear Waste Matters [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	382	374
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	3	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	31	45
Fair Value	354	329
Ameren Missouri | Equity securities
Nuclear Waste Matters [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	191	177
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	603	455
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax	7	14
Equity Securities, FV-NI	787	618
Ameren Missouri | Cash and cash equivalents
Nuclear Waste Matters [Line Items]
Marketable Securities	5	8
Cash and cash equivalents	0	0
Cash and Cash Equivalents and Restricted Cash and Cash Equivalents	0	0
Cash and cash equivalents	5	8
Ameren Missouri | Other Debt And Equity Securities
Nuclear Waste Matters [Line Items]
Net Receivables (Payables) From Pending Securities Sales, Interest, and Securities Purchases, Cost Basis	4	3
Net Receivables (Payables) From Pending Securities Sales, Interest, And Securities Purchases, Available-For-sale Securities, Accumulated Gross Unrealized Gain, Before Tax	0	0
Net Receivables (Payables) From Pending Securities Sales, Interest, And Securities Purchases, Available-For-sale Securities, Accumulated Gross Unrealized Loss, Before Tax	0	0
Net Receivables (Payables) From Pending Securities Sales, Interest, and Securities Purchases, Fair Value	$ 4	$ 3